1. Field of the Invention
The present invention relates to an LSI system with a plurality of LSIs having different scan systems and provided on an identical printed circuit board. More particularly, it relates to a technique of connecting each scan system to each other in the LSI system.
2. Description of the Related Art
Conventionally, scan systems of various types have been employed to effect an operation or function test of an LSI. In a known scan system, the scan operation is carried out by connecting a group of flip-flops provided on an LSI in series with each other, inputting scan data from a scan data-in (SI) terminal allocated to an input pin of the LSI, and effecting a serial transfer of data through each flip-flop, for example, using two-phase clocks of A-phase and B-phase.
On the other hand, as another form different from the above scan system, LSIs which adopt a JTAG-Boundary Scan system (Standard-IEEE P1149.1) using two signals of a test clock (TCK) signal and a test mode select (TMS) signal have been recently increased.
The JTAG-Boundary Scan system (hereinafter simply referred to as "JTAG") includes, in addition to the above data scan system, a boundary scan system having a group of flip-flops (Boundary Scan Register, hereinafter referred to as "BS register") which are provided in the vicinity of input/output portions of an LSI and which are connected in series with each other, and an instruction register scan system having a group of flip-flops (Instruction Register, hereinafter referred to as "IR register") which are connected in series with each other and in which instructions for effecting a test are set. In the JTAG, the scan operation is carried out by selecting a test mode by a test mode select (TMS) signal, inputting scan data from a test data-in (TDI) terminal allocated to an input pin of the LSI to each scan system, and effecting a serial transfer of data through each flip-flop using a test clock (TCK).
Recently, there are often cases in that both LSIs having scan systems using the above two-phase (A/B) clocks (hereinafter referred to as "A/B-LSI") and LSIs having JTAGs (hereinafter referred to as "JTAG-LSI") are mounted on an identical printed circuit board. Namely, an LSI system in which LSIs having different scan systems are provided on a single printed circuit board has been developed.
However, in a known LSI system in which LSIs having different scan systems are provided on an identical printed circuit board, each scan system has been provided for the corresponding one of the LSIs, independently of other scan systems.
Accordingly, such an LSI system poses a number of problems in that: first, the number of external terminals to be provided on a printed circuit board for a scan operation is relatively increased; second, procedures for effecting the respective scan operations must be taken individually for each of the LSIs; and third, the procedures are complicated and thus it takes long time for the scan operation.
Note, the problems in the prior art will be explained later in detail in contrast with the preferred embodiments of the present invention.